Evolution of the Astronomical Eyepiece - Brayebrook Observatory

EVOLUTION of the ASTRONOMICAL EYEPIECE
ZEIS S WI DE-ANGLE (OR IGIN
UNKNOWN) - A 2-3-1-1 form having a
63˚ field and 0.7Fe eye clearance. The
glasses used were boro-silicate hard
crown and extra-dense flint.
EURYSCOPIC III - A Kellner type of
wide field eyepiece manufactured by
the Ferson Optical Company of Biloxi,
Missi ssippi. (Euryscopi c: from the
Greek: to see wide). The separation of
field and eye lens was reduced, and the
field lens equi-convex. This widened
the field to 50˚ at f/4. Eye relief was the
same at 0.46Fe.
B E R TELE - Desi gned for Steinheil
by L u dw ig Ja kob Bertele (19 00-
1 9 8 5 ) . Th e pate nt describes an
ey epiece of 1- 1-2 f or m, inte nd ed
f or use in mi lit ary b in ocula rs, a nd
therefore somewhat over-corrected. I t
pos sesses a 70˚ f ield at f/ 5 and
eye re li ef 0. 8Fe. A cco rd ing to th e
d e s i g n e r, “ its advantage lay in the
elimina tion of every deterio ratin g
influenc e of the curva ture (of the
fi el d), b ut abo ve a ll in the supp re s -
s io n of la rge air sp aces. I n the
main th e improvement is however
ob tained owin g to th e u se of a
s t rongly bent ocula r lens of menis -
cus shape. ” The gla sses used are
SK2, FK5 and SF12. The design is
no ted for its re markable o rt hoscopy.
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